1. Field of the Invention
This invention relates in general to novel polyurea and polycarbamate compositions and mixtures thereof useful as release agents for the manufacture of release liners and pressure-sensitive adhesive tapes. More particularly, it relates to pressure-sensitive adhesive tapes incorporating these release agents as a coating on their backing member.
2. Description of the Prior Art
Release agents for pressure-sensitive adhesive tapes, are, in general, used to prevent, or at least reduce, the transfer of the adhesive mass during unwind from a roll thereof, to the backing member, and to control the unwind tension. A release coat provides suitable release properties only if it is less adherent to the adhesive mass than is the backing member itself. However, the release coat must have sufficient adhesion to the backing member to prevent "pick-off" thereof by the adhesive mass. And, it must have a suitable amount of adhesion to the adhesive mass otherwise it will unwind too readily when in roll form. Thus, it is seen that a release coating to be suitable must involve a balancing of various desired characteristics. It has been found, however, that with some release agents, although initially good release characteristics are provided; after extended contact with an adhesive mass, particularly at elevated temperatures, undesirable side effects are noted. Thus, the adhesion between the release coat and adhesive mass may be so great as to make unwinding very difficult, if not impossible. Various other disadvantages associated with the use of release agents now known to the prior art are also known.
It is known in the art to use certain poly N-acyl-imines as release agents for adhesive tapes. For example, U.S. Pat. Nos. 3,475,196 and 3,590,017 describe release agents comprising poly N-acyl-imines prepared by the reaction of a polyalkylene imine such as polyethylene imine with a straight chain isocyanate such as stearyl isocyanate. U.S. Pat. Nos. 3,394,799; 3,510,342; and 3,282,727 describe similar products useful as release agents. However, release agents of this type do not provide the advantageous properties associated with the release agents of this invention. Thus, the novel class of release agents, as disclosed hereinafter, provides a pressure-sensitive adhesive tape which unwinds satisfactorily after storage even in a warm environment, and the adhesive exhibits substantially unimpaired tack and adhesion.